It has been discovered that the medical outcome for a patient suffering from severe brain trauma or from ischemia caused by stroke or heart attack or cardiac arrest is improved if the patient is cooled below normal body temperature (37° C.). Furthermore, it is also accepted that for such patients, it is important to prevent hyperthermia (fever) even if it is decided not to induce hypothermia. Moreover, in certain applications such as post-CABG surgery, it might be desirable to rewarm a hypothermic patient.
As recognized by the present invention, the above-mentioned advantages in regulating temperature can be realized by cooling or heating the patient's entire body. Moreover, the present invention understands that since many patients already are intubated with central venous catheters for other clinically approved purposes anyway such as drug delivery and blood monitoring, providing a central venous catheter that can also cool or heat the blood requires no additional surgical procedures for those patients. The following U.S. patents, all of which are incorporated herein by reference, disclose various intravascular catheters/systems/methods: U.S. Pat. Nos. 6,749,625, 6,419,643, 6,416,533, 6,409,747, 6,405,080, 6,393,320, 6,368,304, 6,338,727, 6,299,599, 6,290,717, 6,287,326, 6,165,207, 6,149,670, 6,146,411, 6,126,684, 6,306,161, 6,264,679, 6,231,594, 6,149,676, 6,149,673, 6,110,168, 5,989,238, 5,879,329, 5,837,003, 6,383,210, 6,379,378, 6,364,899, 6,325,818, 6,312,452, 6,261,312, 6,254,626, 6,251,130, 6,251,129, 6,245,095, 6,238,428, 6,235,048, 6,231,595, 6,224,624, 6,149,677, 6,096,068, 6,042,559, and U.S. patent application Ser. No. 10/355,776. Less optimally, surface cooling can be used. U.S. Pat. Nos. 6,827,728, 6,818,012, 6,802,855, 6,799,063, 6,764,391, 6,692,518, 6,669,715, 6,660,027, 6,648,905, 6,645,232, 6,620,187, 6,461,379, 6,375,674, 6,197,045, and 6,188,930 (collectively, “the external pad patents”), all of which are incorporated herein by reference, disclose such surface cooling systems. In both intravascular catheters and external pad systems, coolant such as a gas or saline is circulated through the heat exchange element.
Regardless of the particular heat exchange element that is engaged with the patient, it is clear that heat must be removed from or added to the coolant that flows through the heat exchange element. The present invention makes the following critical observations. Typically, the coolant from the catheter or pad flows through a heat transfer apparatus which warms or cools the coolant using a secondary fluid. The heat transfer apparatus may include a cartridge or bag or other device through which the coolant flows, and the cartridge or bag or other device may be immersed in a secondary fluid bath, with the secondary fluid in the bath exchanging heat with the coolant. Examples of such systems are set forth in some of the above-referenced patents.
As understood herein, when medical personnel engage the coolant bag or cartridge with the secondary fluid bath, the secondary fluid bath may be exposed, and for this reason, in the event that a single electrical fault exists in the system, it is desirable that the bath be grounded for operator safety. The present invention critically recognizes, however, that once the bath is no longer accessible because the primary coolant bag or cartridge is engaged with it, it is desirable from a patient standpoint that the bath not be grounded, in case any leakage current might flow for various fault-related reasons from the pad or catheter.